The activities of hypothalamic single units will be recorded via etched, floating, microwire electrodes in unanesthetized, unrestrained animals. The responses of these units to hypothalamic and to skin temperatures will be recorded as a function of wakefulness, slow wave sleep, REM sleep, and circadian time. The influence of melatonin on sleep, body temperature regulation, and daily torpor and seasonal changes in these influences will be studied in round tailed ground squirrels. Changes in the characteristics of hypothalamic thermosensitivity which are responsible for the daily body temperature cycle will be studied to determine the relative contributions of sleep/wakefulness influences and separate circadian influences.